Field of Technology
The present invention relates generally to the sensing of surgical fluid levels and/or a fluid level flow rate to determine relative remaining fluid levels and transmit warnings when fluid levels are below a predetermined threshold.
Description of the Background
The optical elements of the eye include both a cornea (at the front of the eye) and a lens within the eye. The lens and cornea work together to focus light onto the retina at the back of the eye. The lens also changes in shape, adjusting the focus of the eye to vary between viewing near objects and far objects. The lens is found just behind the pupil and within a capsular bag, the capsular bag being a thin, relatively delicate structure which separates the eye into anterior and posterior chambers.
With age, clouding of the lens or cataracts is fairly common. Cataracts may form in the hard central nucleus of the lens, in the softer peripheral cortical portion of the lens, or at the back of the lens near the capsular bag. Cataracts can be treated by the replacement of the cloudy lens with an artificial lens. Phacoemulsification systems often use ultrasound energy to fragment the lens and aspirate the lens material from within the capsular bag. This may allow the capsular bag to be used for positioning of the artificial lens, and maintains the separation between the anterior portion of the eye and the vitreous humor in the posterior chamber of the eye.
During cataract surgery and other therapies of the eye, accurate control over the volume of fluid within the eye is highly beneficial. For example, while ultrasound energy breaks up the lens and allows it to be drawn into a treatment probe with an aspiration flow, a corresponding irrigation flow may be introduced into the eye so that the total volume of fluid in the eye does not change excessively. If the total volume of fluid in the eye is allowed to get too low at any time during the procedure, the eye may collapse and cause significant tissue damage. Similarly, excessive pressure within the eye may strain and injure tissues of the eye.
While a variety of specific fluid transport mechanisms may be used in phacoemulsification and other treatment systems for the eyes, aspiration flow systems can generally be classified in two categories: 1) volumetric-based aspiration flow systems using positive displacement pumps (e.g. peristaltic); and 2) vacuum-based aspiration systems using a vacuum source, typically applied to the aspiration flow through an air-liquid interface within a reservoir (e.g. Venturi). Both systems may be incorporated into one treatment system and/or cassette. Cassette (“pack”) systems can be used to couple peristaltic pump drive rotors and/or vacuum systems of the surgical consoles to an eye treatment handpiece, with the flow network conduit of the cassette being disposable to avoid cross-contamination between different patients.
In traditional ophthalmic surgery, fluid from the fluid source is also used to irrigate the eye during a procedure. As mentioned above, the irrigation fluid serves to maintain proper intraocular pressure and to replace fluid during aspiration of emulsified lens fragments. The irrigation source is typically a 500 ml bottle or drip bag of saline solution. One issue is that, during ophthalmic surgery, the potential exists for the saline solution to be depleted, turning the irrigation dry. Though an unlikely scenario, the potential consequences are substantial—severe cornmeal burns, capsular tear requiring vitrectomy or additional vitro-retinal surgery, damage to the structure of the eye, and/or loss of vision.
To mitigate such occurrences, staff operating a system typically begin each procedure with a fresh irrigation source prior to each case, and monitor the fluid visually throughout surgery. In some instances, flow sensors are used to measure flow out of the irrigation source. However, conventional configurations do not efficiently provide relative irrigation source volumes and only provide warnings when a detected flow indicates a very low irrigation source volume. As such, improvements are needed in the art to address these issues.